1. Field of the Invention
The present invention relates in general to a semiconductor switching device and, more particularly, to a voltage-controlled type semiconductor switching device which controls the amount of current flowing therethrough in accordance with the electric field to be created by a voltage applied between electrodes of the switching device.
2. Discussion of Background
The working speed of a semiconductor integrated circuit is limited fundamentally due to the carrier mobility. Various techniques have been studied to provide an integrated circuit (IC) device utilizing a compound semiconductor, such as GaAs, Al.sub.x Ga.sub.1-x As, or the like in which the electron mobility is higher than that of Si. At present, an electron mobility of up to about 8,000 cm.sup.2 /V.multidot.sec can be obtained at room temperature. In addition, a technique for cooling an IC device with liquid nitrogen has been proposed to improve electron mobility by a factor of ten or more over conventional devices, thereby increasing the working speed of an IC device.
On the other hand, a known complementary type IC arrangement including n- and p-channel transistors is useful for low electric power consumption of semiconductor IC devices. Complementary IC devices are also excellent in terms of noise margin. However, the working speed of such a complementary type IC device is limited by the lower value between the electron mobility and hole mobility. When the compound semiconductor of the groups III-V (GaAs, etc.) is used in the IC device, the hole mobility is in general merely up to hundreds of cm.sup.2 /V.multidot.sec at room temperature and. This value is lower than the electron mobility. Therefore, even if the IC device is constituted using GaAs, the feature of high electron mobility will not be utilized which makes it difficult to produce a high working speed IC device. Moreover, there is a problem with the manufacturing process of the complementary IC devices using n- and p-channel transistors as they are more complicated than IC devices using single conductive channel transistors.
A field-effect device having a multi-heterojunction using three semiconductor layers is disclosed in Esaki et al., "Polytype Superlattices and Multi-Heterojunctions", Japanese Journal of Applied Physics, Vol. 20, No. 7, (July, 1981), pps. L529-L532. In this device, by applying an external voltage to the specific semiconductor layer, the characteristic of this layer is changed between the semiconductor characteristic and the semimetallic characteristic. Carriers are accumulated in the well of potential thus generated in the semiconductor layer, thereby controlling the current flow along the longitudinal direction of the layer. According to the field-effect device by Esaki et al., however, the carriers are needed to get over the potential barrier caused between two layers in the ON-OFF (i.e. switching) operation mode, and it takes a long time to get over the potential barrier. As a result, there is a limitation for shortening of the switching operation time. Furthermore, in this device, it is impossible to realize the good current cut-off state (with zero current) corresponding to the OFF-state of the transistor.
According to a velocity-modulation transistor of Sakaki, "Velocity-Modulation Transistor", Japanese Journal of Applied Physics, Vol. 21, No. 6 (June, 1982), pps. L381-L383, two separate channels A, B having two different mobilities are formed between source and drain of the article, as shown in FIG. 1. By applying a voltage between the channels, the carriers are allowed to move in another channel having smaller mobility, thereby enabling to control of the current flowing between source and drain. However, according to Sakaki et al., the transistor is constructed in such a manner that (a small amount of) low-mobility carriers continue to flow in the channel in the current cut-off state (i.e., in the OFF-state of the transistor). Thus, it cannot be expected to provide good switching operation to selectively turn the current ON and OFF. According to the velocity-modulation transistor, the concept of turning the current ON and OFF (namely, the effort of setting N=0 in the second term of equation (2)) is not considered.